Method for controlling of valve timing of continuous variable valve duration engine

ABSTRACT

The method for controlling valve timing for a turbo engine includes: classifying control regions depending on an engine speed and an engine load; applying a maximum duration to an intake valve and applying a long duration to an exhaust valve in a first control region; applying the maximum duration to the intake and applying the long duration to the exhaust valve in a second control region; applying the long duration to the exhaust valve and advancing an intake valve closing (IVC) timing in the third control region; applying a short duration to the exhaust valve and controlling the IVC timing in the fourth control region; controlling a wide open throttle valve (WOT) and applying the short duration to the exhaust valve in the fifth control region; controlling a WOT and controlling the IVC timing by applying the long duration to the exhaust valve in the sixth control region.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2015-0176786, filed on Dec. 11, 2015, the entirecontents of which are incorporated herein by reference.

FIELD

The present disclosure relates to a system and a method for controllingvalve timing of a continuous variable valve duration engine.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

An internal combustion engine combusts mixed gas in which fuel and airare mixed at a predetermined ratio through a set ignition mode togenerate power by using explosion pressure.

Generally, a camshaft is driven by a timing belt connected with acrankshaft that converts linear motion of a cylinder by the explosionpressure into rotating motion to actuate an intake valve and an exhaustvalve, and while the intake valve is opened, air is suctioned into acombustion chamber, and while an exhaust valve is opened, gas which iscombusted in the combustion chamber is exhausted.

To improve the operations of the intake valve and the exhaust valve andthereby improve engine performance, a valve lift and a valveopening/closing time (timing) may be controlled according to arotational speed or load of an engine. Therefore, a continuous variablevalve duration (CVVD) device controlling the opening duration of anintake valve and an exhaust valve of the engine and a continuousvariable valve timing (CVVT) device controlling the opening and closingtiming of the intake valve and the exhaust valve of the engine have beendeveloped.

The CVVD device may control opening duration of the valve. In addition,the CVVT device may advance or retard the opening or closing timing ofthe valve in a state that the opening duration of the valve is fixed.That is, if the opening timing of the valve is determined, the closingtiming is automatically determined according to the opening duration ofthe valve.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the present disclosureand therefore it may contain information that does not form the priorart that is already known to a person of ordinary skill in the art.

SUMMARY

The present disclosure provides a system and a method for controllingvalve timing of a continuous variable valve duration engine thatsimultaneously controls duration and timing of the valve being equippedwith a continuous variable valve duration device and a continuousvariable valve timing device disposed on an intake valve side, and beingequipped with a two-stage variable valve duration device and continuousvariable valve timing device disposed on an exhaust valve side of aturbo engine vehicle.

A method for controlling valve timing of a turbo engine provided with acontinuous variable valve duration (CVVD) device and a continuousvariable valve timing (CVVT) device disposed on an intake valve side,and provided with a two-stage variable valve duration (VVD) device andcontinuous variable valve timing (CVVT) device disposed on an exhaustvalve side may include classifying a plurality of control regionsdepending on an engine speed and an engine load. The plurality ofcontrol regions may include: a first control region when the engine loadis less than a first predetermined load; a second control region whenthe engine load is greater than or equal to the first predetermined loadand less than a second predetermined load; a third control region whenthe engine load is greater than or equal to the second predeterminedload and less than a third predetermined load; a fourth control regionwhen the engine load is greater than or equal to the secondpredetermined load and the engine speed is greater than or equal to afirst predetermined speed and less than a second predetermined speed; afifth control region when the engine load is greater than or equal tothe third predetermined load and the engine speed is less than the firstpredetermined speed; and a sixth control region when the engine load isgreater than or equal to the third predetermined load and the enginespeed is greater than or equal to the second predetermined speed.

The method for controlling valve timing further includes: applying amaximum duration to the intake valve and applying a long duration to theexhaust valve to control a valve overlap between the exhaust valve andthe intake valve in the first control region; applying the maximumduration to the intake and applying the long duration to the exhaustvalve in order to control the control overlap according to an engineload in the second control region; applying the long duration to theexhaust valve and advancing an intake valve closing (IVC) timing in thethird control region; applying a short duration to the exhaust valve andcontrolling the intake valve closing (IVC) timing close to a bottom deadcenter in the fourth control region; controlling a wide open throttlevalve (WOT) and applying the short duration to the exhaust valve togenerate scavenging in the fifth control region; controlling a wide openthrottle valve (WOT) and controlling the intake valve closing (IVC)timing by applying the long duration to the exhaust valve so as toreduce a knocking in the sixth control region.

If the control region is in the first control region, then thecontroller may control an intake valve opening (IVO) timing, the intakevalve closing (IVC) timing, and an exhaust valve opening (EVO) to befixed and an exhaust valve closing (EVC) timing to be set up at amaximum value within sustainable combustion stability.

If the control region is in the second control region, then thecontroller may control an exhaust valve closing (EVC) timing to beretard as the engine load is increased in order to increase the valveoverlap, and after when the engine load is greater than or equal to apredetermined load, the controller may control the exhaust valve closing(EVC) timing to be advanced in order to decrease the valve overlap.

If the control region is in the third control region, then thecontroller may advance the intake valve closing (IVC) timing close to abottom dead center when the engine speed is less than a predeterminedspeed, the controller may advance the intake valve closing (IVC) timingto after the bottom dead center when the engine speed is greater than orequal to the predetermined speed.

If the control region is in the fourth control region, then thecontroller may control an intake valve opening (IVO) timing and anexhaust valve closing (EVC) timing to approach at a top dead center inorder to reduce the valve overlap.

If the control region is in the fifth control region, then thecontroller may advance an intake valve opening (IVO) timing to before atop dead center to generate the scavenging and control the intake valveclosing (IVC) timing to after a bottom dead center.

If the control region is in the fifth control region, then thecontroller may advance an intake valve opening (IVO) timing to before atop dead center to generate the scavenging and controls the intake valveclosing (IVC) timing to after a bottom dead center.

If the control region is in the sixth control region, then thecontroller may advance an exhaust valve opening (EVO) timing to before abottom dead center to inhibit or prevent an exhaust pumping and to lowerboost pressure, and the controller controls an exhaust valve closing(EVC) timing to be close to a top dead center.

A system for controlling valve timing of a continuous variable valveduration engine provided with a turbo charger may include a datadetector detecting data related to a running state of the vehicle; acamshaft position sensor detecting a position of a camshaft; an intakecontinuous variable valve duration (CVVD) device controlling an openingtime of an intake valve of the engine; an exhaust two-stage variablevalve duration (VVD) device controlling an opening time of the exhaustvalve of the engine; an intake continuous variable valve timing (CVVT)device controlling an opening and closing timing of the intake valve ofthe engine; an exhaust continuous variable valve timing (CVVT) devicecontrolling an opening and closing timing of the exhaust valve of theengine; and a controller configured to classify a plurality of controlregions depending on an engine speed and an engine load based on signalsfrom the data detector and camshaft position sensor, and configured tocontrol the intake CVVD and CVVT devices, and the exhaust two-stage VVDand CVVT devices according to the control regions, and the a pluralityof control regions may include a first control region when the engineload is less than a first predetermined load; a second control regionwhen the engine load is greater than or equal to the first predeterminedload and less than a second predetermined load; a third control regionwhen the engine load is greater than or equal to the secondpredetermined load and less than a third predetermined load; a fourthregion when the engine load is greater than or equal to the secondpredetermined load and the engine speed is greater than or equal to afirst predetermined speed and less than a second predetermined speed; afifth region when the engine load is greater than or equal to the thirdpredetermined load and the engine speed is less than the firstpredetermined speed; and a sixth region when the engine load is greaterthan or equal to the third predetermined load and the engine speed isgreater than or equal to the second predetermined speed.

The controller may apply a maximum duration to the intake valve andapply the long duration to the exhaust valve to limit a valve overlap inthe first control region, apply the maximum duration to the intake andapply the long duration to the exhaust valves in order to control thecontrol overlap according to the engine load in the second controlregion, apply the long duration to the exhaust valve and advances anintake valve closing (IVC) timing in the third control region, apply theshort duration to the exhaust valve and controls the intake valveclosing (IVC) timing close to a bottom dead center in the fourth controlregion, control a wide open throttle valve (WOT) and apply the shortduration to the exhaust valve to generate scavenging in the fifthcontrol region, and control a wide open throttle valve (WOT) and controlthe intake valve closing (IVC) timing by applying the long duration tothe exhaust valve to reduce knocking in the sixth control region.

The controller may control an intake valve opening (IVO) timing, theintake valve closing (IVC) timing, and an exhaust valve opening (EVO) tobe fixed and an exhaust valve closing (EVC) timing to be set up at amaximum value within sustainable combustion stability in the firstregion.

The controller may control an exhaust valve closing (EVC) timing to beretard as the engine load is increased in order to increase the valveoverlap, when the engine load is greater than or equal to apredetermined load, the controller may control the exhaust valve closing(EVC) timing to be advanced in order to decrease the valve overlap inthe second control region.

The controller may advance the intake valve closing (IVC) timing to beclose to a bottom dead center when the engine speed is less than apredetermined speed, the controller may advance the intake valve closing(IVC) timing to after the bottom dead center when the engine speed isgreater than or equal to the predetermined speed in the third controlregion.

The controller may control an intake valve opening (IVO) timing and anexhaust valve closing (EVC) timing to approach at a top dead center inorder to reduce the valve overlap in the fourth control region.

The controller may advance an intake valve opening (IVO) timing tobefore a top dead center to generate the scavenging and controls theintake valve closing (IVC) timing to after a bottom dead center in thefifth control region.

The controller may retard an exhaust valve opening (EVO) timing to aftera bottom dead center so as to reduce interference of exhaust and controlan exhaust valve closing (EVC) timing to after a top dead center tomaintain catalyst temperature in the fifth control region.

The controller may advance an exhaust valve opening (EVO) timing tobefore a bottom dead center to inhibit or prevent an exhaust pumping andto lower boost pressure, and the controller controls an exhaust valveclosing (EVC) timing to be close to a top dead center in the sixthcontrol region.

As described above, duration and timing of the continuous variable valveare simultaneously controlled, so the engine may be controlled underdesirable conditions.

That is, since opening timing and closing timing of the intake valve andthe exhaust valve are appropriately controlled, the fuel efficiencyunder a partial load condition and engine performance under a high loadcondition are improved. In addition, a starting fuel amount may bereduced by increasing a valid compression ratio, and exhaust gas may bereduced by shortening time for heating a catalyst.

In addition, the cost reduction and power performance may be realized byproviding the two-stage VVD device to the exhaust valve side.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

In order that the disclosure may be well understood, there will now bedescribed various forms thereof, given by way of example, referencesbeing made to the accompanying drawings, in which:

FIG. 1 is a schematic block diagram showing a system for controllingvalve timing of a continuous variable valve duration engine according toone form of the present disclosure;

FIG. 2 is a perspective view showing a continuous variable valveduration device and a continuous variable valve timing device which aredisposed on an intake valve side, and a two-stage variable valveduration device and continuous variable valve timing device which aredisposed on an exhaust valve side;

FIGS. 3A and FIG. 3B are flowcharts showing a method for controllingvalve timing of a continuous variable valve duration engine according toone form of the present disclosure;

FIGS. 4A-4C are graphs showing duration, opening timing, and closingtiming of an intake valve depending on an engine load and an enginespeed according to the present disclosure; and

FIGS. 5A-5C are graphs showing duration, opening timing, and closingtiming of an exhaust valve depending on an engine load and an enginespeed according to the present disclosure.

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Itshould be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

As those skilled in the art would realize, the described forms may bemodified in various different ways, all without departing from thespirit or scope of the present disclosure.

Throughout this specification and the claims which follow, unlessexplicitly described to the contrary, the word “comprise” and variationssuch as “comprises” or “comprising” will be understood to imply theinclusion of stated elements but not the exclusion of any otherelements.

It is understood that the term “vehicle” or “vehicular” or other similarterms as used herein is inclusive of motor vehicles in general includinghybrid vehicles, plug-in hybrid electric vehicles, and other alternativefuel vehicles (e.g., fuels derived from resources other than petroleum).As referred to herein, a hybrid electric vehicle is a vehicle that hastwo or more sources of power, for example a gasoline-powered andelectric-powered vehicle.

Additionally, it is understood that some of the methods may be executedby at least one controller. The term controller refers to a hardwaredevice that includes a memory and a processor configured to execute oneor more steps that should be interpreted as its algorithmic structure.The memory is configured to store algorithmic steps, and the processoris specifically configured to execute said algorithmic steps to performone or more processes which are described further below.

Furthermore, the control logic of the present disclosure may be embodiedas non-transitory computer readable media on a computer readable mediumcontaining executable program instructions executed by a processor, acontroller, or the like. Examples of computer readable media include,but are not limited to, ROM, RAM, compact disc (CD)-ROMs, magnetictapes, floppy disks, flash drives, smart cards, and optical data storagedevices. The computer readable recording medium can also be distributedin network coupled computer systems so that the computer readable mediais stored and executed in a distributed fashion, e.g., by a telematicsserver or a controller area network (CAN).

FIG. 1 is a schematic block diagram showing a system for controllingvalve timing of a continuous variable valve duration engine according toone form of the present disclosure.

An engine according one form of the present disclosure may be a turboengine provided with a turbocharger.

As shown in FIG. 1, a system for controlling valve timing of acontinuous variable valve duration engine includes: a data detector 10,a camshaft position sensor 20, a controller 30, an intake continuousvariable valve duration (CVVD) device 40, an intake continuous variablevalve timing (CVVT) device 45, an exhaust two-stage variable valveduration device 50, and an exhaust continuous variable valve timing(CVVT) device 55.

The data detector 10 detects data related to a running state of avehicle for controlling the intake continuous variable valve duration(CVVD) device 40, the intake continuous variable valve timing (CVVT)device 45, the exhaust two-stage variable valve duration (VVD) device50, and the exhaust continuous variable valve timing (CVVT) device 55.The data detector 10 includes: a vehicle speed sensor 11, an enginespeed sensor 12, an oil temperature sensor 13, an air flow sensor 14,and an accelerator pedal position sensor (APS) 15, although othersensors may be employed.

The vehicle speed sensor 11 detects a vehicle speed, transmits acorresponding signal to the controller 30, and may be mounted at a wheelof the vehicle.

The engine speed sensor 12 detects a rotation speed of the engine from achange in phase of a crankshaft or camshaft, and transmits acorresponding signal to the controller 30.

The oil temperature sensor (OTS) 13 detects temperature of oil flowingthrough an oil control valve (OCV), and transmits a corresponding signalto the controller 30.

The oil temperature detected by the oil temperature sensor 13 may bedetermined by measuring a coolant temperature using a coolanttemperature sensor mounted at a coolant passage of an intake manifold.Therefore, in one form, the oil temperature sensor 13 may include acoolant temperature sensor, and the oil temperature should be understoodto include the coolant temperature.

The air flow sensor 14 detects an air amount drawn into the intakemanifold, and transmits a corresponding signal to the controller 30.

The accelerator pedal position sensor (APS) 15 detects a degree in whicha driver pushes an accelerator pedal, and transmits a correspondingsignal to the controller 30. The position value of the accelerator pedalmay be 100% when the accelerator pedal is pressed fully, and theposition value of the accelerator pedal may be 0% when the acceleratorpedal is not pressed at all.

A throttle valve position sensor (TPS) that is mounted on an intakepassage may be used instead of the accelerator pedal position sensor 15.Therefore, in one form, the accelerator pedal position sensor 15 mayinclude a throttle valve position sensor, and the position value of theaccelerator pedal should be understood to include an opening value ofthe throttle valve.

The camshaft position sensor 20 detects a change of a camshaft angle,and transmits a corresponding signal to the controller 30.

FIG. 2 is a perspective view showing a continuous variable valveduration device and a continuous variable valve timing device which isdisposed on an intake valve side, and a two-stage variable valveduration device and continuous variable valve timing device which isdisposed on an exhaust valve side.

The intake continuous variable valve duration (CVVD) device 40 controlsan opening time of an intake valve of the engine according to a signalfrom the controller 30, the exhaust continuous variable valve duration(CVVD) device 50 controls an opening time of an exhaust valve of theengine according to a signal from the controller 30.

The exhaust two-stage variable valve duration (VVD; Variable ValveDuration) device 50 may control an opening time of the exhaust valve ofengine according to a signal from the controller 30 by switching theopening time to two stage. That is, the exhaust two-stage VVD device 50may use a solenoid valve without a motor and a sensor which is providedto an exhaust CVVD, thereby the manufacturing cost may be reduced.

When exhaust duration is longer, the fuel efficiency and a high-speedperformance may be improved, however a low-speed performance may bedeteriorated. Thereby, a short duration for the low-speed performanceand a long duration for the high-speed performance should be set byexperiment. For example the short duration may be approximately 180-210degrees and the long duration may be approximately 240-250 degrees.

Thereby, the exhaust two-stage VVD device 50 may apply the shortduration or long duration to the exhaust valve by switching.

The exhaust continuous variable valve timing (CVVT) device 55 controlsopening and closing timing of the exhaust valve of the engine accordingto a signal from the controller 30.

The controller 30 may classify a plurality of control regions dependingon an engine speed and an engine load based on signals from the datadetector 10 and camshaft position sensor 20, and control the intake CVVDand CVVT devices 40 and 45, and the exhaust two-stage VVD and CVVTdevices 50 and 55 according to the control regions. Here, the pluralityof control regions may be classified into six control regions.

The controller 30 applies a maximum duration to the intake valve andapplies the long duration to the exhaust valve to limit a valve overlapin the first control region, applies the maximum duration to the intakeand applies the long duration to the exhaust valves in order to controlthe control overlap according to the engine load in the second controlregion, applies the long duration to the exhaust valve and advances anintake valve closing (IVC) timing in the third control region, appliesthe short duration to the exhaust valve and controls the intake valveclosing (IVC) timing close to a bottom dead center in the fourth controlregion, controls a wide open throttle valve (WOT) and applies the shortduration to the exhaust valve to generate scavenging in the fifthcontrol region, and controls a wide open throttle valve (WOT) andcontrols the intake valve closing (IVC) timing by applying the longduration to the exhaust valve to reduce knocking in the sixth controlregion.

For these purposes, the controller 30 may be implemented as at least oneprocessor that is operated by a predetermined program, and thepredetermined program may be programmed in order to perform each step ofa method for controlling valve timing of a continuous variable valveduration engine according to the present disclosure.

Various forms described herein may be implemented within a recordingmedium that may be read by a computer or a similar device by usingsoftware, hardware, or a combination thereof, for example.

The hardware of the forms described herein may be implemented by usingat least one of application specific integrated circuits (ASICs),digital signal processors (DSPs), digital signal processing devices(DSPDs), programmable logic devices (PLDs), field programmable gatearrays (FPGAs), processors, controllers, micro-controllers,microprocessors, and electrical units designed to perform any otherfunctions.

The software such as procedures and functions of the forms described inthe present disclosure may be implemented by separate software modules.Each of the software modules may perform one or more functions andoperations described in the present disclosure. A software code may beimplemented by a software application written in an appropriate programlanguage.

Hereinafter, a method for controlling valve timing of a continuousvariable valve duration engine according to one form of the presentdisclosure will be described in detail with reference to FIGS. 3A toFIG. 5C.

FIG. 3A and FIG. 3B are flowcharts showing a method for controllingvalve timing of a continuous variable valve duration engine.

FIGS. 4A-4C are graphs showing duration, opening timing, and closingtiming of an intake valve depending on an engine load and an enginespeed, and FIGS. 5A-5C are graphs showing duration, opening timing, andclosing timing of an exhaust valve depending on an engine load and anengine speed.

As shown in FIG. 3A and FIG. 3B, a method for controlling valve timingof a continuous variable valve duration engine starts with classifying aplurality of control regions depending on an engine speed and an engineload by the controller 30 at step S100.

The control regions will be described with reference to FIGS. 4A-4C andFIGS. 5A-5C. The first to sixth control regions are indicated in theFIG. 4A to FIG. 5C.

The controller 30 may classify control regions as a first control regionwhen the engine load is less than a first predetermined load, a secondcontrol region when the engine load is greater than or equal to thefirst predetermined load and less than a second predetermined load, anda third control region when the engine load is greater than or equal tothe second predetermined load and less than a third predetermined load.In addition, the controller 30 may classify control regions as a fourthregion when the engine load is greater than or equal to the secondpredetermined load and the engine speed is greater than or equal to afirst predetermined speed and less than a second predetermined speed, afifth region when the engine load is greater than or equal to the thirdpredetermined load and the engine speed is less than the firstpredetermined speed, and a sixth region when the engine load is greaterthan or equal to the third predetermined load and the engine speed isgreater than or equal to the second predetermined speed.

Meanwhile, referring to FIGS. 4A-4C and FIGS. 5A-5C, a crank angle ismarked in an intake valve duration (IVD) map and an exhaust valveduration (EVD) map, which indicating the opening time of the intakevalve and exhaust valve. For example, regarding the IVD map in FIG. 4A,a curved line written as a number 200 at inner side of the fourth regionmeans that the crank angle is approximately 200 degrees, a curved linedmarked as a number 220 at outer side of the number 200 means that thecrank angle is approximately 220 degrees. Although not shown in thedrawing, the crank angle which is approximately more than approximately200 degrees and less than approximately 220 degrees is positionedbetween the curved line of the number 200 and the curved line of thenumber 220.

In addition, a unit of number designated in an intake valve opening(IVO) timing map is before a top dead center (TDC), a unit of numberdesignated in an intake valve closing (IVC) timing map is after a bottomdead center (BDC), a unit of number designated in an exhaust valveopening (EVO) timing map is before BDC, and a unit of number designatedin an exhaust valve closing (EVC) map is after TDC.

Each region and curved line in FIGS. 4A to FIG. 5C are one form of thepresent disclosure, it may be modified within the technical idea andscope of the present disclosure.

Referring to FIGS. 3A to 5C, the control regions are classifiedaccording to the engine speed and load in the step of S100. After that,the controller 30 determines whether the engine state is under the firstcontrol region at step S110.

In the step of S110, if the engine load is less than a firstpredetermined load, the controller 30 determines that the engine stateis under the first control region. At this time, the controller 30applies a maximum duration to the intake valve and applies the longduration to the exhaust valve to control a valve overlap between theexhaust valve and intake valve at step S120. The valve overlap is astate where the intake valve is opened and the exhaust valve is notclosed yet.

In other words, when the engine is under low load, then the controller30 may control both the intake valve opening (IVO) timing and the intakevalve closing (IVC) timing being fixed such that the intake valve has amaximum duration value. As shown in FIGS. 4A-4C, the first controlregion may be approximately 0 to 10 degrees before TDC in the IVO timingmap and approximately 100 to 110 degrees after BDC in the IVC timingmap.

Also, the controller 30 may control the EVO timing to be fixed and setup the EVC timing. Meanwhile, as the valve overlap is increased, thefuel consumption is cut, whereas the combustion stability isdeteriorated. Accordingly, properly setting the valve overlap isdesired. However, according to the present disclosure, it is possible toget highly improved fuel-efficiency by setting desired valve overlap up,which fixing the EVO timing and controlling the EVC timing to be set upat a maximum value within sustainable combustion stability. The timingvalue may be determined by a predetermined map.

For example, as shown in FIGS. 5A-5C, the EVO timing may be fixed atapproximately 40 to 50 degrees before BDC, the EVC timing may beestablished by moving the degrees thereof in an after TDC direction. TheEVC timing may be a maximum value such that the combustion stability issustainable.

When the current engine state does not belong to the first controlregion at the step S110, the controller 30 determines whether thecurrent engine state belongs to the second control region at step S130.

In the step of S130, if the engine load is more than or equal to thefirst predetermined load and less than the second predetermined load,the controller 30 determines that the engine state is under the secondcontrol region. At this time, controller 30 applies the maximum durationto the intake valve and applies the long duration to the exhaust valvein order to control the control overlap according to the engine load atstep S140.

The controller 30 may control EVC timing to be late in a direction aftera top dead center as the engine load reaches a predetermined load,thereby the control overlap may be increased.

Herein, the intake pumping is decreased as the EVC timing is controlledto be late in a direction after the top dead center, however the exhaustpumping is increased as the EVO timing approaches to the bottom deadcenter. Therefore, the controller 30 controls the increased controloverlap to be shorten by advancing the EVC timing to the lockingposition when the engine load is increased more than the predeterminedload.

In addition, the controller 30 may control the IVC timing at the LIVCposition (Late Intake Valve Closing; an angle of approximately 100-110degrees after BDC) by applying a maximum duration to the intake valve inorder to inhibit or prevent from the knocking as the engine load isincreased

When the current engine state does not belong to the second controlregion at the step S130, the controller 30 determines whether thecurrent engine state belongs to the third control region at step S150.

In the step of S150, if the engine load is more than or equal to thesecond predetermined load and less than the third predetermined load,the controller 30 determines that the engine state is under the thirdcontrol region. At this time, controller 30 applies the long duration tothe exhaust valve and advances an intake valve closing (IVC) timing atstep S160.

The IVC timing is controlled at the LIVC position (Late Intake ValveClosing; an angle of approximately 100-110 degrees after BDC, referringto FIGS. 4A-4C) in the first and second control regions. By the way,since the IVC timing is retarded at the LIVC position, the averagepressure in the intake manifold (boost pressure) may be increased andthe knocking is generated as the engine load is increased. Accordingly,the fuel efficiency may be deteriorated. Therefore, the controller 30advances the IVC timing to inhibit or prevent effect as described abovein the third control region which has relatively higher load.

At this time, the controller 30 may rapidly advance the IVC timing closeto BDC when the engine speed is less than the predetermined speed so asto reflect characteristic of the turbo engine, as shown in FIGS. 4A-4C.In addition, if the engine speed is greater or equal to thepredetermined speed, the controller 30 may slowly advance the IVC timingat an angle of approximately 30-50 degrees after BDC because the boostpressure is relatively lower. The predetermined speed may beapproximately 1500 rpm.

As shown in FIGS. 5A-5C, the long duration is applied to the exhaustvalve of both the second control region and the third control region.The long duration of exhaust valve may be set at approximately 240-250so as to decrease exhaust pumping and increase the control overlap.

When the current engine state does not belong to the third controlregion at the step S150, the controller 30 determines whether thecurrent engine state belongs to the fourth control region at step S170.

If the engine state is under the fourth control region in the S170, thecontroller 30 applies the short duration to the exhaust valve andcontrols the intake valve closing (IVC) timing close to the bottom deadcenter at step S180.

The fourth control region may be a low boost region that the engine loadis greater than or equal to the second predetermined load and the enginespeed is greater than or equal to the first predetermined speed and lessthan the second predetermined speed. For example, the firstpredetermined speed may be approximately 1500 rpm, and the secondpredetermined speed may be approximately 2500 rpm.

The controller 30 controls the IVC timing close to BDC due to improvingfuel efficiency in the fourth region, which is in the low boost region.In addition, the controller 30 may shorten the valve overlap between theintake valve and the exhaust valve and improve the combustion stabilityby approaching the IVO timing and EVC timing close to the TDC. For thispurpose, controller 30 may apply the short duration to the exhaust valveinstead of the long duration.

Resultantly, the short duration (e.g., approximately 180 degrees) may beapplied to the intake and exhaust valve in the fourth control region.

When the current engine state does not belong to the fourth controlregion at the step S170, the controller 30 determines whether thecurrent engine state belongs to the fifth control region at step S190.

In the S190, if the engine load is greater than or equal to the thirdpredetermined load and the engine speed is greater than or equal to thefirst predetermined speed, then the controller 30 determines that theengine state is under the fifth control region. At this time, controller30 controls a wide open throttle valve (WOT) and applies the shortduration to the exhaust valve to generate scavenging at step S200.

In the turbo engine, if the throttle valve is controlled to be wide open(WOT) when the engine speed is less than the first predetermined speed(e.g., 1500 rpm), intake port pressure becomes higher than exhaust portpressure by boosting. Therefore, an effect of a scavenging phenomenonwhich emits combustion gas of the exhaust is prominent in the turboengine compared to a natural aspirated engine.

Accordingly, as shown in FIGS. 4A-4C, the controller 30 may advance theIVO timing at an angle of approximately 20-40 degrees before BDC togenerate the scavenging, and control the IVC timing at angle ofapproximately 0-20 degrees after BDC.

Moreover, as shown in FIGS. 5A-5C, the controller 30 may sufficientlyretard the EVO timing to after BDC so as to maximally generate thescavenging by reducing interference of exhaust. Furthermore, the EVCtiming may be controlled within an angle of approximately 30 degreesafter TDC in order to maintain catalyst temperature. Accordingly, theshort duration is applied to the exhaust valve in the fifth controlregion.

When the current engine state does not belong to the fifth controlregion at the step S190, the controller 30 determines whether thecurrent engine state belongs to the sixth control region at step S210.

In the step of S210, if the engine load is greater than or equal to thethird predetermined load and the engine speed is greater than or equalto the second predetermined speed, then the controller determines theengine state is under the sixth control region. At this time, controller30 controls a wide open throttle valve (WOT), controls the intake valveclosing (IVC) timing by applying the long duration to the exhaust valveso as to reduce exhaust pumping and knocking by lowering the boostpressure at step S220.

When the engine speed is greater than the second predetermined speed(e.g., approximately 2500 rpm) in the sixth control region, thescavenging phenomenon disappears because exhaust port pressure is muchhigher than intake port pressure. Therefore, as shown in FIGS. 5A-5C,the controller 30 advances the EVO timing an angle of approximately 30degrees before BDC and approaches the EVC timing close to the TDC toinhibit or prevent an exhaust pumping. At this time, the controller 30may apply the long duration to the exhaust valve instead of the shortduration which is used in the fifth control region by switching.

Meanwhile, when WOT control is performed at a high speed condition,knocking is rarely generated in the natural aspirated engine, on thecontrary, knocking may be deteriorated in the turbo engine. Thus, asshown in FIGS. 4A-4C, the controller 30 may advance the IVC timingwithin an angle of approximately 50 degrees after BDC to reduce knockingby decreasing boost pressure.

As described above, duration and timing of the continuous variable valveare simultaneously controlled, so the engine may be controlled underdesired conditions.

That is, since opening timing and closing timing of the intake valve andthe exhaust valve are appropriately controlled, the fuel efficiencyunder a partial load condition and engine performance under a high loadcondition are improved. In addition, a starting fuel amount may bereduced by increasing a valid compression ratio, and exhaust gas may bereduced by shortening time for heating a catalyst.

In addition, the cost reduction and power performance may be realized byproviding the two-stage VVD device to the exhaust valve side.

While this present disclosure has been described in connection with whatis presently considered to be practical exemplary forms, it is to beunderstood that the present disclosure is not limited to the disclosedforms. On the contrary, it is intended to cover various modificationsand equivalent arrangements included within the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for controlling valve timing of a turboengine provided with a continuous variable valve duration (CVVD) deviceand a continuous variable valve timing (CVVT) device disposed on anintake valve side, and provided with a two-stage variable valve duration(VVD) device and a continuous variable valve timing (CVVT) devicedisposed on an exhaust valve side, the method comprising: classifying,by a controller, a plurality of control regions depending on an enginespeed and an engine load, wherein the plurality of control regionscomprises: a first control region determined by the controller when theengine load is less than a first predetermined load, a second controlregion determined by the controller when the engine load is greater thanor equal to the first predetermined load and less than a secondpredetermined load, a third control region determined by the controllerwhen the engine load is greater than or equal to the secondpredetermined load and less than a third predetermined load, a fourthcontrol region when the engine load is greater than or equal to thesecond predetermined load and the engine speed is greater than or equalto a first predetermined speed and less than a second predeterminedspeed, a fifth control region when the engine load is greater than orequal to the third predetermined load and the engine speed is less thanthe first predetermined speed, and a sixth control region when theengine load is greater than or equal to the third predetermined load andthe engine speed is greater than or equal to the second predeterminedspeed; applying, by the controller, a maximum duration to an intakevalve and applying a long duration to an exhaust valve to control avalve overlap between the exhaust valve and the intake valve in thefirst control region; applying, by the controller, the maximum durationto the intake valve and applying the long duration to the exhaust valveso as to control a control overlap according to an engine load in thesecond control region; applying, by the controller, the long duration tothe exhaust valve and advancing an intake valve closing (IVC) timing inthe third control region; applying, by the controller, a short durationto the exhaust valve and controlling the intake valve closing (IVC)timing close to a bottom dead center in the fourth control region;controlling, by the controller, a wide open throttle valve (WOT) andapplying the short duration to the exhaust valve to generate scavengingin the fifth control region; and controlling, by the controller, a wideopen throttle valve (WOT) and controlling the intake valve closing (IVC)timing by applying the long duration to the exhaust valve so as toreduce a knocking in the sixth control region.
 2. The method of claim 1,wherein, when the first control region is determined, the controllercontrols an intake valve opening (IVO) timing, the intake valve closing(IVC) timing, and an exhaust valve opening (EVO) to be fixed and anexhaust valve closing (EVC) timing to be set up at a maximum valuewithin sustainable combustion stability.
 3. The method of claim 1,wherein, when the second control region is determined, the controllercontrols an exhaust valve closing (EVC) timing to be retard as theengine load is increased so as to increase the valve overlap, and afterwhen the engine load is greater than or equal to a predetermined load,the controller controls the exhaust valve closing (EVC) timing to beadvanced to decrease the valve overlap.
 4. The method of claim 1,wherein, when the third control region is determined, the controlleradvances the intake valve closing (IVC) timing close to a bottom deadcenter when the engine speed is less than a predetermined speed, thecontroller advances the intake valve closing (IVC) timing to after thebottom dead center when the engine speed is greater than or equal to thepredetermined speed.
 5. The method of claim 1, wherein, when the fourthcontrol region is determined, the controller controls an intake valveopening (IVO) timing and an exhaust valve closing (EVC) to approach at atop dead center so as to reduce the valve overlap.
 6. The method ofclaim 1, wherein, when the fifth control region is determined, thecontroller advances an intake valve opening (IVO) timing to before a topdead center to generate the scavenging and controls the intake valveclosing (IVC) timing to after the bottom dead center.
 7. The method ofclaim 1, wherein, when the fifth control region is determined, thecontroller retards an exhaust valve opening (EVO) timing to after abottom dead center so as to reduce interference of exhaust and controlsan exhaust valve closing (EVC) timing to after a top dead center tomaintain a catalyst temperature.
 8. The method of claim 1, wherein, whenthe sixth control region is determined, the controller advances anexhaust valve opening (EVO) timing to before a bottom dead center toinhibit an exhaust pumping and to lower boost pressure, and thecontroller controls an exhaust valve closing (EVC) timing to be close toa top dead center.
 9. A system for controlling valve timing of acontinuous variable valve duration engine provided with a turbo charger,the system comprising: a data detector configured to detect data relatedto a running state of a vehicle; a camshaft position sensor configuredto detect a position of a camshaft; an intake continuous variable valveduration (CVVD) device configured to control an opening time of anintake valve of the engine; an exhaust two-stage variable valve duration(VVD) device configured to control an opening time of an exhaust valveof the engine; an intake continuous variable valve timing (CVVT) deviceconfigured to control an opening and closing timing of the intake valveof the engine; an exhaust continuous variable valve timing (CVVT) deviceconfigured to control an opening and closing timing of the exhaust valveof the engine; and a controller configured to classify a plurality ofcontrol regions depending on an engine speed and an engine load based onsignals from the data detector and camshaft position sensor, andconfigured to control the intake CVVD and CVVT devices, and the exhausttwo-stage VVD and CVVT devices according to the plurality of controlregions, wherein the plurality of control regions comprises: a firstcontrol region determined by the controller when the engine load is lessthan a first predetermined load, a second control region determined bythe controller when the engine load is greater than or equal to thefirst predetermined load and less than a second predetermined load, athird control region determined by the controller when the engine loadis greater than or equal to the second predetermined load and less thana third predetermined load, a fourth region determined by the controllerwhen the engine load is greater than or equal to the secondpredetermined load and the engine speed is greater than or equal to afirst predetermined speed and less than a second predetermined speed, afifth region determined by the controller when the engine load isgreater than or equal to the third predetermined load and the enginespeed is less than the first predetermined speed, and a sixth regionwhen the engine load is greater than or equal to the third predeterminedload and the engine speed is greater than or equal to the secondpredetermined speed, and wherein the controller applies a maximumduration to the intake valve and applies the long duration to theexhaust valve to limit a valve overlap in the first control region,applies the maximum duration to the intake and applies the long durationto the exhaust valves so as to control a control overlap according tothe engine load in the second control region, applies the long durationto the exhaust valve and advances an intake valve closing (IVC) timingin the third control region, applies a short duration to the exhaustvalve and controls the intake valve closing (IVC) timing close to abottom dead center in the fourth control region, controls a wide openthrottle valve (WOT) and applies the short duration to the exhaust valveto generate scavenging in the fifth control region, and controls a wideopen throttle valve (WOT) and controls the intake valve closing (IVC)timing by applying the long duration to the exhaust valve to reduceknocking in the sixth control region.
 10. The system of claim 9, whereinthe controller controls an intake valve opening (IVO) timing, the intakevalve closing (IVC) timing, and an exhaust valve opening (EVO) to befixed and an exhaust valve closing (EVC) timing to be set up at amaximum value within sustainable combustion stability in the firstregion.
 11. The system of claim 9, wherein the controller controls anexhaust valve closing (EVC) timing to be retard as the engine load isincreased so as to increase the valve overlap, when the engine load isgreater than or equal to a predetermined load, the controller controlsthe exhaust valve closing (EVC) timing to be advanced so as to decreasethe valve overlap in the second control region.
 12. The system of claim9, wherein the controller advances the intake valve closing (IVC) timingto be close to a bottom dead center when the engine speed is less than apredetermined speed, the controller advances the intake valve closing(IVC) timing to after the bottom dead center when the engine speed isgreater than or equal to the predetermined speed in the third controlregion.
 13. The system of claim 9, wherein the controller controls anintake valve opening (IVO) timing and an exhaust valve closing (EVC) toapproach at a top dead center so as to reduce the valve overlap in thefourth control region.
 14. The system of claim 9, wherein the controlleradvances an intake valve opening (IVO) timing to before a top deadcenter to generate the scavenging and controls the intake valve closing(IVC) timing to after a bottom dead center in the fifth control region.15. The system of claim 9, wherein the controller retards an exhaustvalve opening (EVO) timing to after a bottom dead center so as to reduceinterference of exhaust and controls an exhaust valve closing (EVC)timing to after a top dead center to maintain a catalyst temperature inthe fifth control region.
 16. The system of claim 9, wherein thecontroller advances an exhaust valve opening (EVO) timing to before abottom dead center to inhibit an exhaust pumping and to lower boostpressure, and the controller controls an exhaust valve closing (EVC)timing to be close to a top dead center in the sixth control region.